The present invention relates to rotary-wing aircraft such as helicopters. More specifically, the invention is directed to a system and a method for providing anti-torque and yaw control in a rotary-wing aircraft without the use of a conventional tail rotor.
Tail rotors are the most prevalent means for providing yaw control, and for overcoming the biasing torque generated by the main rotor in rotary-wing aircraft such as helicopters. Tail rotors, however, possess a number of substantial disadvantages. For example, tail rotors present a serious safety risk to ground personnel working in the vicinity of rotary-wing aircraft. In addition, inadvertent contact between tail rotors and stationary objects on the ground causes a substantial number of accidents each year. Tail rotors also necessitate the use of multiple bearings, right-angle gearboxes, and high-speed shafting, and thus raise reliability and maintainability issues.
Furthermore, small arms fire and projectiles from other types of weapons can incapacitate a tail rotor, leading to a sudden and total loss of anti-torque and yaw control and rendering the aircraft uncontrollable. This vulnerability is of particular concern in military aircraft. In addition, the tail rotor makes a substantial contribution to the overall acoustic signature of a rotary-wing aircraft, adds significantly to pilot workload, and can make a rotary-wing aircraft difficult to control in cross-wind conditions.
Tail rotors also possess substantial disadvantages from the standpoint of energy consumption. In particular, the power needed to operate a tail rotor usually represents a significant portion, e.g., fifteen percent, of a rotary-wing aircraft""s overall shaft-horsepower requirement. Thus, the use of a tail rotor necessitates a larger power plant than would otherwise be required, and increases the overall fuel consumption of the aircraft.
Systems that eliminate the need for a tail rotor have been developed. For example, U.S. Pat. Nos. 3,059,877; 4,200,2523; and 4,948,068, each of which is incorporated by reference herein in its entirety, describe anti-torque and yaw-control systems based on the principle of circulation control (also referred to as xe2x80x9ccirculation-control blowingxe2x80x9d). Circulation control is an aerodynamic phenomenon in which a bulk flow around a body is deflected by a sheet of air ejected tangentially to the surface of the body. The deflection of the bulk flow generates a force on the body in a direction opposite the deflected flow.
Circulation control in a rotary-wing aircraft is achieved using pressurized air from the aircraft""s engine, or an auxiliary fan mounted within the fuselage. The pressurized air is ejected from downwardly-facing slots in the right side of the aircraft""s aft fuselage, or tail boom. The resulting jets or sheets of air follow the contour of the tail boom, and deflect the downwash from the main rotor as it travels over the tail boom. This deflection produces a lateral force on the tail boom that partially counters the torque generated by the main rotor.
The systems disclosed in the above-noted patents, in general, do not produce sufficient force to filly counter the biasing torque of the main rotor. Thus, reaction jets are typically used to supplement the anti-torque force generated using circulation-control. More specifically, one or more jets of pressurized air are discharged in a lateral direction through nozzles mounted on the rearward portion of the tail boom. These jets produce a lateral force that counteracts the main rotor torque. The reaction jets also provide the yaw control previously furnished by the tail rotor. In particular, the reaction jets are capable of being throttled in response to pilot input. This feature permits the force produced by the jets (and, therefore, the net lateral force on the aircraft) to be varied, thereby facilitating yaw control.
Anti-torque and yaw-control systems based on circulation control permit a rotary-wing aircraft to be operated without most of the disadvantages associated with tail rotors. The reaction jets used in these systems, however, require a substantial amount of energy to operate. In fact, the energy requirements of reaction jets are roughly equivalent to those of a conventional tail rotor of comparable capabilities. Hence, aircraft that use circulation-control-techniques for anti-torque and yaw control, in general, require power-plants of approximately the same capacity and consume roughly equivalent amounts of fuel as comparable tail-rotor aircraft.
Reducing the overall power requirements of a rotary-wing aircraft can provide substantial benefits. For example, lowering the power requirements of an aircraft facilitates the use of smaller, lighter engines that consume lower amounts of fuel. These reductions can produce corresponding increases in the range and payload capacity of the aircraft. Alternatively, the power formerly dedicated to the tail rotor or jet thrusters can be used to drive a pusher fan located at the rear of the aircraft, thereby allowing the aircraft to achieve a higher maximum forward velocity than would otherwise be possible.
As indicated by the above discussion, an ongoing need exists for an anti-torque and yaw-control system that eliminates the need for a tail rotor, and that requires less energy to operate than current systems which provide anti-torque and yaw control without the use of a tail rotor.
A presently-preferred embodiment of the invention provides a rotary-wing aircraft comprising a main rotor, a tail boom extending through an area of downwash from the main rotor, and a first linear nozzle fixedly coupled to the tail boom. The first linear nozzle has an opening extending along the tail boom, and is adapted to discharge a sheet of fluid in a direction substantially tangential to an outer surface of the tail boom. The rotary-wing aircraft also comprises a yaw-control member movably coupled to the tail boom, and a second linear nozzle fixedly coupled to the tail boom. The second linear nozzle has an opening extending along the tail boom, and is adapted to discharge a sheet of fluid in a direction substantially tangential to an outer surface of the yaw-control member.
Another presently-preferred embodiment of the invention provides a rotary-wing aircraft comprising a fuselage, a main rotor rotatably coupled to the fuselage, and a tail boom fixedly coupled to the fuselage so that a least a portion of the tail boom is located within an area of downwash from the main rotor. The rotary-wing aircraft also comprises a yaw-control member movably coupled to a lower portion of the tail boom, and a linear nozzle mounted on the tail boom and having an opening extending along the tail boom. The linear nozzle is adapted to discharge a sheet of fluid in a direction substantially tangential to an outer surface of the tail boom and toward the yaw-control member.
Another presently-preferred embodiment of the invention provides an anti-torque and yaw-control system for a rotary-wing aircraft having a main rotor and a tail boom located in an area of downwash from the main rotor. The system comprises a yaw-control member adapted to be movably coupled to the tail boom, and a first linear nozzle adapted to discharge a jet of fluid in a direction substantially tangential to an outer surface of the tail boom to produce a layer of fluid flow that extends along the outer surface. The system further comprises a second linear nozzle adapted to discharge a jet of fluid in a direction substantially tangential to an outer surface of the yaw-control member to produce a layer of fluid flow that extends along the outer surface of the yaw-control member.
Another presently-preferred embodiment of the invention provides a rotary-wing aircraft comprising a main rotor, a tail boom extending through an area of downwash from the main rotor, and a linear nozzle fixedly coupled to the tail boom. The linear nozzle has an opening extending along the tail boom, and is adapted to discharge a jet of fluid in a direction substantially tangential to an outer surface of the tail boom to produce a layer of fluid flow along at least a portion of the outer surface thereby altering a direction of the main-rotor downwash. The rotary-wing aircraft also comprises a yaw-control member coupled to the tail boom and being selectviely positionable in response to input from a pilot of the rotary-wing aircraft to further alter a direction of the main-rotor downwash and thereby facilitate yaw control of the rotary-wing aircraft.
Another presently-preferred embodiment of the invention provides a rotary-wing aircraft comprising a main rotor, a tail boom extending through an area of downwash from the main rotor, and a first linear nozzle fixedly coupled to the tail boom. The first linear nozzle has an opening extending along the tail boom, and is adapted to discharge a sheet of fluid in a direction substantially tangential to an outer surface of the tail boom. The rotary-wing aircraft further comprises a yaw-control member movably coupled to the tail boom, and a second linear nozzle fixedly coupled to the yaw-control member. The second linear nozzle has an opening extending along the yaw-control member, and is adapted to discharge a sheet of fluid in a direction substantially tangential to an outer surface of the yaw-control member.
A presently-preferred method of counteracting main-rotor torque and controlling yaw in a helicopter having a main rotor and a tail boom located within an area of downwash from the main rotor comprises altering a direction of travel of the main-rotor downwash by directing a jet of fluid along an outer surface of the tail boom to produce a layer of fluid flow along at least a portion of the outer surface, and further altering the direction of travel of the main-rotor downwash by deflecting the layer of fluid flow using a movable yaw-control member coupled to the tail boom.
Another presently-preferred method of counteracting main-rotor torque and controlling yaw in a rotary-wing aircraft having a main rotor and a tail boom located within an area of downwash from the main rotor comprises forming a first layer of fluid flow along an outer surface of the tail boom by directing a first sheet of fluid in a direction substantially tangential to the outer surface, and forming a second layer of fluid flow along an outer surface of a movable yaw-control member coupled to the tail boom by discharging a second sheet of fluid in a direction substantially tangential to the outer surface of the yaw-control member using a second linear nozzle.